Wireless power transfer pad with ferrite chimney

ABSTRACT

A wireless power transfer (“WPT”) pad with a ferrite chimney is disclosed. The WPT pad includes a winding with a conductor where the conductor is wound in a planar configuration. The winding includes a center section about which the winding is wound. The WPT pad includes a ferrite structure with a parallel section located on a side of the winding with at least a portion in parallel with the winding, and a chimney section in magnetic contact with the parallel section and located in the center section of the winding, the chimney section extending perpendicular to the parallel section.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/554,950 entitled “WIRELESS POWER TRANSFER PAD WITHFERRITE CHIMNEY” and filed on Sep. 6, 2017 for Patrice Lethellier, andU.S. Provisional Patent Application No. 62/554,960 entitled “WIRELESSPOWER TRANSFER PAD WITH FERRITE PYRAMID-SHAPED CHIMNEY” and filed onSep. 6, 2017 for Patrice Lethellier, the entire contents of which areincorporated herein by reference for all purposes.

FIELD

This invention relates to wireless power transfer and more particularlyrelates to wireless power transfer pads.

BACKGROUND

Wireless power transfer is becoming increasingly popular. Wireless powertransfer involves transmitting power from a primary pad located on astationary wireless power transfer device, such as a charging station,to a secondary pad on a mobile device, such as an electric vehicle, overa significant gap. The gap typically includes an air gap and can besignificant. For example, the air gap may be from ground level to asecondary pad located under a vehicle. An air gap in the range of sixinches to 10 inches is not uncommon. As the amount of power transferredover an air gap increases, voltages for transmission and receptionsystems has increased. One method of wireless power transfer includesusing a resonant tank, which often boosts voltages of a wireless powertransfer pad, which increases voltage ratings of components used for theequipment. As voltages increase, electromagnetic field strengthsincrease, which may pose a danger to people exposed to theelectromagnetic radiation. Various methods are used in wireless powertransfer to direct electromagnetic fields in a particular direction andto increase efficiency of the wireless power transfer.

SUMMARY

A wireless power transfer (“WPT”) pad with a ferrite chimney isdisclosed. The WPT pad includes a winding with a conductor where theconductor is wound in a planar configuration. The winding includes acenter section about which the winding is wound. The WPT pad includes aferrite structure with a parallel section located on a side of thewinding with at least a portion in parallel with the winding, and achimney section in magnetic contact with the parallel section andlocated in the center section of the winding, the chimney sectionextending perpendicular to the parallel section.

Another WPT pad, in some embodiments, includes a winding with aconductor where the conductor is wound in a planar configuration and thewinding includes a center section about which the winding is wound. TheWPT pad includes a ferrite structure that includes a parallel sectionlocated on a side of the winding with at least a portion in parallelwith the winding and a chimney section in magnetic contact with theparallel section and located in the center section of the winding. Thechimney section extends perpendicular to the parallel section. Thechimney section is positioned adjacent to the winding in the centersection of the winding. The ferrite structure includes an exteriorsection located exterior to an outside edge of the winding. The outsideedge of the ferrite section is distal to an inside edge adjacent to thecenter section of the winding. The exterior section is in magneticcontact with the parallel section and extends perpendicular to theparallel section. The chimney section and the exterior section eachextend in a direction from the parallel section toward the winding and adistance at least a thickness of the winding, where the thickness ismeasured in a direction perpendicular to the ferrite structure.

A WPT system includes a resonant converter that receives power from apower source and a WPT pad connected to the resonant converter, wherethe WPT pad receives power from the resonant converter. The WPT padincludes a ferrite structure with a parallel section located on a sideof the winding with at least a portion in parallel with the winding, anda chimney section in magnetic contact with the parallel section andlocated in the center section of the winding, where the chimney sectionextends perpendicular to the parallel section.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem with a wireless power transfer (“WPT”) pad with a ferritechimney;

FIG. 2 is a schematic block diagram illustrating one embodiment of apower converter apparatus;

FIG. 3A is a schematic block diagram plan view of one embodiment of aWPT pad with a ferrite chimney in a center of the WPT pad;

FIG. 3B is a schematic block diagram section view of WPT padsrepresented in FIG. 3A;

FIG. 4A is a schematic block diagram plan view of one embodiment of aWPT pad with a ferrite chimney in a center and exterior edge of the WPTpad;

FIG. 4B is a schematic block diagram section view of WPT padsrepresented in FIG. 4A;

FIG. 5A is a schematic block diagram plan view of one embodiment of atwo winding WPT pad with a ferrite chimney in a center and exterior edgeof the WPT pad;

FIG. 5B is a schematic block diagram section view of WPT padsrepresented in FIG. 5A;

FIG. 6 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad; and

FIG. 7 is a schematic block diagram illustrating a plan view of theembodiment of a low voltage WPT pad of FIG. 6.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment, but mean “one or more but not all embodiments” unlessexpressly specified otherwise. The terms “including,” “comprising,”“having,” and variations thereof mean “including but not limited to”unless expressly specified otherwise. An enumerated listing of itemsdoes not imply that any or all of the items are mutually exclusiveand/or mutually inclusive, unless expressly specified otherwise. Theterms “a,” “an,” and “the” also refer to “one or more” unless expresslyspecified otherwise.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details areprovided, such as examples of programming, software modules, userselections, network transactions, database queries, database structures,hardware modules, hardware circuits, hardware chips, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention may bepracticed without one or more of the specific details, or with othermethods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

A wireless power transfer (“WPT”) pad with a ferrite chimney isdisclosed. The WPT pad includes a winding with a conductor where theconductor is wound in a planar configuration. The winding includes acenter section about which the winding is wound. The WPT pad includes aferrite structure with a parallel section located on a side of thewinding with at least a portion in parallel with the winding, and achimney section in magnetic contact with the parallel section andlocated in the center section of the winding, the chimney sectionextending perpendicular to the parallel section.

In some embodiments, the chimney section extends in a direction from theparallel section toward the winding and a distance at least a thicknessof the winding, where the thickness is measured in a directionperpendicular to the parallel section of the ferrite structure. In otherembodiments, the chimney section extends a distance beyond the thicknessof the winding. In other embodiments, the chimney section is positionedadjacent to the winding in the center section of the winding. In otherembodiments, the ferrite structure includes an exterior section locatedexterior to an outside edge of the winding. The outside edge is distalto an inside edge adjacent to the center section of the winding, wherethe exterior section is in magnetic contact with the parallel sectionand extends perpendicular to the parallel section. In a furtherembodiment, the exterior section extends in a direction from theparallel section toward the winding and a distance at least a thicknessof the winding. The thickness is measured in a direction perpendicularto the ferrite structure.

In some embodiments, the chimney section includes a gap where one ormore components of the WPT pad are located in the center section of thewinding and one or more conductors from the winding to the one or morecomponents extend through the gap. In further embodiments, the one ormore components include one or more capacitors. In other embodiments, anend of the winding is located at an exterior edge of the center sectionand is wound in a circular pattern that expands from a center pointwithin the center section where each succeeding lap of the winding isexternal to a previous lap of the winding. In further embodiments, eachlap of the winding is within a same plane and the plane is parallel tothe parallel section of the ferrite structure.

In some embodiments, the WPT pad includes two or more windings whereeach winding includes a parallel section of a ferrite structureassociated with the winding and a center section. Each center sectionincludes a chimney section of the ferrite structure associated with thewinding. In further embodiments, the ferrite structures of each of thetwo or more windings are adjacent to each other and are magneticallycoupled. In other embodiments, the WPT pad is a transmitter pad thattransmits power wirelessly to a secondary pad or secondary pad thatreceives power wirelessly from a transmitter pad. In other embodiments,the WPT pad is part of a wireless power transfer system that transferspower wirelessly to a vehicle.

Another WPT pad, in some embodiments, includes a winding with aconductor where the conductor is wound in a planar configuration and thewinding includes a center section about which the winding is wound. TheWPT pad includes a ferrite structure that includes a parallel sectionlocated on a side of the winding with at least a portion in parallelwith the winding and a chimney section in magnetic contact with theparallel section and located in the center section of the winding. Thechimney section extends perpendicular to the parallel section. Thechimney section is positioned adjacent to the winding in the centersection of the winding. The ferrite structure includes an exteriorsection located exterior to an outside edge of the winding. The outsideedge of the ferrite section is distal to an inside edge adjacent to thecenter section of the winding. The exterior section is in magneticcontact with the parallel section and extends perpendicular to theparallel section. The chimney section and the exterior section eachextend in a direction from the parallel section toward the winding and adistance at least a thickness of the winding, where the thickness ismeasured in a direction perpendicular to the ferrite structure.

In some embodiments, the chimney section includes a gap where one ormore components of the WPT pad are located in the center section of thewinding and one or more conductors from the winding to the one or morecomponents extend through the gap. In other embodiments, the chimneysection and the exterior section each extend a distance beyond thethickness of the winding. In other embodiments, the WPT pad includes twoor more windings where each winding includes a parallel section of aferrite structure associated with the winding and a center section. Eachcenter section includes a chimney section of the ferrite structureassociated with the winding. In other embodiments, the ferritestructures of each of the two or more windings are adjacent to eachother and are magnetically coupled.

A WPT system includes a resonant converter that receives power from apower source and a WPT pad connected to the resonant converter, wherethe WPT pad receives power from the resonant converter. The WPT padincludes a ferrite structure with a parallel section located on a sideof the winding with at least a portion in parallel with the winding, anda chimney section in magnetic contact with the parallel section andlocated in the center section of the winding, where the chimney sectionextends perpendicular to the parallel section.

FIG. 1 is a schematic block diagram illustrating one embodiment of awireless power transfer (“WPT”) system 100 with a WPT pad with a ferritechimney. The WPT system 100 includes a power converter apparatus 104 anda secondary receiver apparatus 106 separated by a gap 108, and a load110, which are described below.

The WPT system 100 includes a power converter apparatus 104 thatreceives power from a power source 112 and transmits power over a gap108 to a secondary receiver apparatus 106, which transfers power to aload 110. The power converter apparatus 104, in one embodiment, includesa resonant converter 118 that receives a direct current (“DC”) voltagefrom a DC bus 116. In one embodiment, the power source 112 provides DCpower to the DC bus 116. In another embodiment, the power source 112 isan alternating current (“AC”) power source, for example from a buildingpower system, from a utility, from a generator, etc. and the powerconverter apparatus 104 includes a form of rectification to provide DCpower to the DC bus 116. For example, the rectification may be in theform of a power factor correction and rectification circuit 114. In theembodiment, the power factor correction and rectification circuit 114may include an active power factor correction circuit, such as aswitching power converter. The power factor correction and rectificationcircuit 114 may also include a full-bridge, a half-bridge rectifier, orother rectification circuit that may include diodes, capacitors, surgesuppression, etc.

The resonant converter 118 may be controlled by a primary controller120, which may vary parameters within the resonant converter 118, suchas conduction time, conduction angle, duty cycle, switching, etc. Theprimary controller 120 may receive information from sensors and positiondetection 122 within or associated with the power converter apparatus104. The primary controller 120 may also receive information wirelesslyfrom the secondary receiver apparatus 106.

The power converter apparatus 104 includes a primary pad 126 thatreceives power from the resonant converter 118. In one embodiment,portions of the resonant converter 118 and primary pad 126 form aresonant circuit that enables efficient wireless power transfer acrossthe gap 108. The gap 108, in some embodiments includes an air gap, butmay also may partially or totally include other substances. For example,where the primary pad 126 is in a roadway, the gap 108 may include aresin, asphalt, concrete, plastic or other material just over thewindings of the primary pad 126 in addition to air, snow, water, etc.between the primary pad 126 and a secondary pad 128 located in thesecondary receiver apparatus 106.

The secondary receiver apparatus 106 includes a secondary pad 128connected to a secondary circuit 130 that delivers power to the load110. The secondary receiver apparatus 106 may also include a secondarydecoupling controller 132 that controls the secondary circuit 130 andmay also be in communication with sensors and/or position detection 136and wireless communications 134 coupled to the power converter apparatus104.

In one embodiment, the secondary receiver apparatus 106 and load 110 arepart of a vehicle 140 that receives power from the power converterapparatus 104. The load 110 may include a battery 138, a motor, aresistive load, a circuit or other electrical load. For example, the WPTsystem 100 may transfer power to a portable computer, a consumerelectronic device, to an industrial load, or other load that wouldbenefit from receiving power wirelessly.

In one embodiment, the secondary circuit 130 includes a portion ofresonant circuit that interacts with the secondary pad 128 and that isdesigned to receive power at a resonant frequency. The secondary circuit130 may also include a rectification circuit, such as a full-bridgerectifier, a half-bridge rectifier, and the like. In another embodiment,the secondary circuit 130 includes a power converter of some type thatreceives power from the resonant circuit/rectifier and actively controlspower to the load 110. For example, the secondary circuit 130 mayinclude a switching power converter. In another embodiment, thesecondary circuit 130 includes passive components and power to the load110 is controlled by adjusting power in the power converter apparatus104. In another embodiment, the secondary circuit 130 includes an activerectifier circuit that may receive and transmit power. One of skill inthe art will recognize other forms of a secondary circuit 130appropriate for receiving power from the secondary pad 128 anddelivering power to the load 110.

The resonant converter 118, in one embodiment, includes an activeswitching section coupled to a resonant circuit formed with componentsof the resonant converter 118 and the primary pad 126. The resonantconverter 118 is described in more detail with regard to FIG. 2.

FIG. 2 is a schematic block diagram illustrating one embodiment of apower converter apparatus 104. The power converter apparatus 104 isconnected to a power source 112 and includes a power factor correctionand rectification circuit 114 connected to a DC bus 116 feeding aresonant converter 118 connected to a primary pad 126 as described withregard to the WPT system 100 of FIG. 1.

The resonant converter 118 includes a switching module 202 and a tuningsection 204. The switching module 202, includes four switches configuredto connect the DC bus 116 and to ground. Typically, switches S1 and S3close while switches S2 and S4 are open and vice-versa. When switches S1and S3 are closed, the DC bus 116 is connected to a positive connectionof the tuning section 204 through inductor L1 a and the ground isconnected to the negative connection of the tuning section 204 throughinductor L1 b while switches S2 and S4 are open. When switches S2 and S4are closed, the ground is connected to the positive terminal of thetuning section 204 and the DC bus 116 is connected to the positiveconnection of the tuning section 204. Thus, the switching modulealternates connection of the DC bus 116 and ground to the tuning sectionsimulating an AC waveform. The AC waveform typically imperfect due toharmonics.

Typically switches S1-S4 are semiconductor switches, such as ametal-oxide-semiconductor field-effect transistor (“MOSFET”), a junctiongate field-effect transistor (“JFET”), a bipolar junction transistor(“BJT”), an insulated-gate bipolar transistor (“IGBT”) or the like.Often the switches S1-S4 include a body diode that conducts when anegative voltage is applied. In some embodiments, the timing of openingand closing switches S1-S4 are varied to achieve various modes ofoperations, such as zero-voltage switching.

The tuning section 204 of the resonant converter 118 and the primary pad126 are designed based on a chosen topology. For example, the resonantconverter 118 and primary pad 126 may form aninductor-capacitor-inductor (“LCL”) load resonant converter, a seriesresonant converter, a parallel resonant converter, and the like. Theembodiment depicted in FIG. 2 includes an LCL load resonant converter.

Resonant converters include an inductance and capacitance that form aresonant frequency. When a switching frequency of the tuning section 204is at or close to the resonant frequency, voltage with the tuningsection 204 and primary pad 126 often increases to voltages levelshigher than the voltage of the DC bus 116. For example, if the voltageof the DC bus 116 is 1 kilovolt (“kV”), voltage in the tuning section204 and resonant converter 118 may be 3 kV or higher. The high voltagesrequire component ratings, insulation ratings, etc. to be high enoughfor expected voltages.

The primary pad 126 includes capacitor C3 and inductor Lp while thetuning section 204 includes series capacitor C2. Capacitors C2 and C3add to provide a particular capacitance that forms a resonant frequencywith inductor Lp. While the apparatus 200 of FIG. 2 is focused on theresonant converter 118 and primary pad 126, the secondary receiverapparatus 106 includes a secondary pad 128 and a secondary circuit 130that typically includes a tuning section where the inductance of thesecondary pad 128 and capacitance of the tuning section of the secondarycircuit 130 form a resonant frequency and the secondary pad 128 andsecondary circuit 130 have voltage issues similar to the primary pad 126and resonant converter 118.

FIG. 3A is a schematic block diagram plan view of one embodiment 300 ofa WPT pad 126, 128 with a ferrite chimney in a center of the WPT pad126, 128. The WPT pad 126, 128 can be a primary pad 126 or a secondarypad 128. FIG. 3B is a schematic block diagram section view of WPT pads126, 128 represented in FIG. 3A, which are the same embodiment 300.

The WPT pads 126, 128 each include a winding 302 parallel to a parallelsection 304 of a ferrite structure. The ferrite structure also includesa center chimney section 306 located in a center section 308 of thewinding 302. The winding 302 includes a conductor wound in a planarconfiguration about the center section 308 about which the winding 302is wound. Typically, the winding 302 is not wound with an empty space inthe center for a variety of reasons. For example, bending radius of theconductor may prevent a tight winding 302 without an open centersection. In another example, including the conductor in the centersection 308 may be less efficient than leaving an open center sectionbecause conductor in the center section 308 may not contributesignificantly to the magnetic field directed toward an opposing pad. Oneof skill in the art will recognize other reasons for an open centersection 308.

FIG. 3B is a cross section of both a primary pad 126 and a secondary pad128. (See Section A-A′, which is representative of both WPT pads 126,128, although in FIG. 3B the section is depicted only on the primary pad126 for clarity.) Both the primary pad 126 and the secondary pad 128 mayhave similar layout as depicted in FIG. 3A. The WPT pads 126, 128 mayinclude separators 316 or some other structure to keep the winding 302in place. The conductors of the winding 302 are depicted in FIG. 3B asround for convenience, but may be oblong, square, rectangular or anothershape and may be litz wire or some other multi-strand conductor.Typically, the winding 302 of the primary pad 126 and the secondary pad128 are facing each other, which helps to direct the magnetic fieldbetween the WPT pads 126, 128. A simplified magnetic pathway 314 isdepicted where the center section forms a north pole and the exterioredges of the WPT pads 126, 128 form a south pole.

Note that the ferrite structure does not extend into the center section308. Often, not much is gained from having ferrite in the centersection. In other embodiments, the center section includes ferritematerial. For example, some embodiments may have a specific structure inthe center section 308, which may assist in misalignment.

While the winding 302 in FIG. 3A is depicted as a single conductor,other configurations may include two or more conductors wound inparallel, which may reduce voltage requirements of the WPT pads 126,128. In one embodiment, the winding 302 is wound in a single layer in aplanar configuration starting at a center point and each wrap is laidexternal to a previous wrap. For example, the winding 302 may be in aEuclidean spiral or in a shape similar to a Euclidean spiral, such asdepicted in FIG. 3A where the spiral of the winding 302 is not circularbut is more square or rectangular shaped. A winding 302 in thisEuclidean spiral-like shape is beneficial for wireless power transfer inshaping an electromagnetic field from a primary pad 126 directed towarda secondary pad 128. In other embodiments, the winding 302 may includetwo or more layers of conductors.

The parallel section 304 is located on a side of the winding 302 with atleast a portion in parallel with the winding 302. The depictedembodiment, as can be seen in FIG. 3B, includes a parallel section 304that is rectangular. Other shapes may be used where at least a portionin parallel with the winding 302. For example, the ferrite structure mayhave split shape as described in U.S. patent application Ser. No.15/456,402 filed Mar. 10, 2016 for Patrice Lethellier, which isincorporated herein by reference for all purposes. In some embodiments,the parallel section 304 of the ferrite structure includes ferrite barsin a radial pattern extending from the center section 308. In otherembodiments, the parallel section 304 is made up of two or more ferriteelements that are in contact with each other or are close enough to forma magnetic pathway through the parallel section 304. One of skill in theart will recognize other designs of a parallel section 304 that includeat least a portion in parallel with the winding 302.

The chimney section 306 is in in magnetic contact with the parallelsection 304 and are located in the center section 308 of the winding302. The chimney section 306 extends perpendicular to the parallelsection 304. Typically, the primary pad 126 and the secondary pad areseparated by a gap 108 where the parallel sections 304 are a distance310 from each other. At the chimney section 306, the distance 312 isreduced within the gap 108. Typically, the electromagnetic fieldstrength in the center section 308 is stronger than in other locations.The ferrite structure provides a magnetic pathway 314 that directs amajority of the electromagnetic field, although some flux lines existoutside the ferrite structure. At the gap 108, the magnetic pathway 314jumps across the gap 108. The chimney section 306 provides a shorteneddistance 312 across the gap 108 where the electromagnetic field strengthis typically strong, which may increase magnetic coupling and anassociated coefficient of coupling between the WPT pads 126, 128.

Typically, the winding 302 is embedded in a material, such as a resin, aplastic, asphalt, etc., which may hold the winding 302 in place and thematerial typically has a thickness. The thickness of the chimney section306, in one embodiment, is a distance at least a thickness of thewinding 302, where the thickness is measured in a directionperpendicular to the parallel section 304 of the ferrite structure. Dueto the thickness of the winding 302, having a chimney section 306 thatis the thickness of the winding 302 or at least to a distance of thewinding 302 beyond the parallel section 304 does not increase a totalthickness of the WPT pads 126, 128. Where the chimney section 306extends away from the parallel section 304 a distance of the thicknessof the winding 302 and/or a distance of the winding 302 beyond theparallel section 304, a covering of the winding 302 may also extendacross the chimney section 306 a same thickness as the covering over thewinding 302.

In another embodiment, the chimney section 306 extends a distance beyonda thickness of the winding 302 and/or a distance of the winding 302beyond the parallel section 304, which further reduces the distance 312of the magnetic pathway 314 through the gap 108. However, in theembodiment the chimney section 306 may be exposed or may have a coveringless thick than the covering over the winding 302.

The chimney section 306 may be designed based on a strength of themagnetic field at the location of the chimney section 306. For example,a width of the chimney section 306 may be sufficient to preventsaturation of the ferrite material used for the chimney section 306. Inthe embodiment depicted in FIG. 3A, the chimney section 306 includesrectangular elements. The rectangular elements may be sized toaccommodate the winding 302. Rectangular elements may be more readilyavailable other shapes and may be used for convenience. In otherembodiments, the rectangular elements may be sized to overlap to form acontinuous chimney section 306. In other embodiments, the chimneysection 306 includes a custom ferrite material shaped in a circle orother convenient shape. One of skill in the art will recognize othershapes of a chimney section 306.

FIG. 4A is a schematic block diagram plan view of one embodiment 400 ofa WPT pad 126, 128 with a ferrite chimney in a center section 308 andalong an exterior edge of the WPT pad 126, 128. FIG. 4B is a schematicblock diagram section view of WPT pads 126, 128 represented in FIG. 4A,which are the same embodiment 400. In the embodiment 400, the WPT pads126, 128 are the same as the embodiment 300 of FIGS. 3A and 3B but theferrite structure includes an exterior section 402 around the perimeterof the parallel section 304. Discussion of the embodiment 300 of FIGS.3A and 3B are substantially applicable to the embodiment 400 of FIGS. 4Aand 4B.

The exterior section 402, in one embodiment, is located exterior to anoutside edge of the winding 302, and the outside edge is distal to aninside edge adjacent to the center section 308 of the winding 302. Theexterior section 402 is in magnetic contact with the parallel section304 and extends perpendicular to the parallel section 304. By includingan exterior section 402, the magnetic pathway 314 is further reduced andmay further increase magnetic coupling and a coupling coefficientbetween the primary pad 126 and the secondary pad 128. In addition, theexterior section 402 may reduce stray electromagnetic radiation in adirection away from the WPT pads 126, 128, which may increase safety,may reduce a need for other shielding, may make passing of governmentalemission standards easier, etc.

Note that the exterior section 402 of FIG. 4A aligns with an exteriorshape of the parallel section 304, which is square. In otherembodiments, the parallel section 304 is shaped as a rectangle, acircle, an oval or other shape and the exterior section 402 may followthe exterior edge of the parallel section 304 or may be shapeddifferently.

As with the chimney section 306, the exterior section 402 may extend ina direction from the parallel section 304 toward the winding 302 and adistance at least a thickness of the winding 302 and/or a distance ofthe winding 302 beyond the parallel section 304, where the thickness ismeasured in a direction perpendicular to the ferrite structure. Inanother embodiment, the exterior section 402 extends a distance beyond athickness of the winding 302 and/or a distance of the winding 302 beyondthe parallel section 304.

In some embodiments, the chimney section 306 includes a gap and one ormore components of the WPT pads 126, 128 are located in the centersection 308 of the winding 302 and one or more conductors from thewindings 302 to the one or more components extend through the gap. Forexample, all or a portion of a ferrite bar of the chimney sections 306in the embodiments 300, 400 of FIGS. 3A and 4A may be removed to allowfor wiring. In one embodiment, the one or more components are one ormore capacitors.

FIG. 5A is a schematic block diagram plan view of one embodiment 500 ofa two winding WPT pad 126, 128 with a ferrite chimney in a centersection 308 and along an exterior edge of the WPT pad (e.g. 126 or 128).FIG. 5B is a schematic block diagram section view of WPT pads 126, 128represented in FIG. 5A, which are the same embodiment 500. In theembodiment, the ferrite structure is adjacent to a first winding 302 anda second winding 502. The windings 302, 502 are connected and are woundto produce a north pole at a center section 308 of a first winding 302and a south pole at the center section 308 of the second winding 502, orvice versa. The windings 302, 502 are adjacent to a parallel section 304of the ferrite structure and include a chimney section 306 for eachwinding 302, 502. As described for the embodiments 300, 400 of FIGS. 3A,3B, 4A and 4B, the distance 312 between chimney sections 306 is lessthan the distance 310 between the parallel sections 304. The magneticpathways 314 are different than the embodiments 300, 400 of FIGS. 3A,3B, 4A and 4B.

FIG. 5B again depicts section views of a primary pad 126 and a secondarypad 128. The windings 302, 502 may include separators 316. The magneticpathways 314 include a north pole at the chimney section 306 of thefirst winding 302 and a south pole at the chimney section 306 of thesecond winding 502 with opposing poles at the edges of the WPT pads 126,128. Dual windings 302, 502 provide advantages in some instances, suchas a stronger electromagnetic field between the windings 302, 502.

One embodiment of WPT pads 126, 128 with two windings 302, 502 (notshown) includes chimney sections 306 for both windings 302, 502 withoutexterior sections 402. In the embodiment 500 depicted in FIGS. 5A and5B, the WPT pads 126, 128 include exterior sections 402 on the exterioredges of the parallel section 304 of the ferrite structure. Note thatone WPT pad (e.g. primary pad 126) may include an exterior section 402while the opposite WPT pad (e.g. secondary pad 128) may exclude exteriorsections 402, or vice versa. As with the other described embodiments300, 400, the center sections 308 may be void of ferrite material insome embodiments, or may include ferrite material in the center sections308. In addition, the parallel section 304 and/or exterior section 402may be shaped differently than shown, as described with regard to theembodiments 300, 400 of FIGS. 3A, 3B, 4A and 4B.

FIG. 6 is a schematic block diagram illustrating one embodiment of a lowvoltage WPT pad. Capacitance that interacts with inductance of thewinding 302 forms a resonant frequency. For example, Capacitors C2 andC3 may be combined into a capacitance Cs. In the embodiment, thecapacitance Cs has been distributed in three capacitors, Cs1, Cs2 andCs3. The winding 302 of the primary pad 126, which forms an inductance,is divided into four sections, Lp1, Lp2, Lp3, Lp4. The capacitors Cs1,Cs2 and Cs3 are distributed between winding sections as depicted. Whilethree capacitors and four winding sections are depicted, one of skill inthe art will recognize that other numbers of capacitors and windingsections may be used. The primary pad 126 depicted in FIG. 6 may be usedto lower voltage of the resonant converter 118 and primary pad 126, andis described further in U.S. patent application Ser. No. 16/103,512filed Aug. 14, 2018 for Patrice Lethellier, which is incorporated hereinby reference for all purposes. The capacitors Cs1, Cs2 and Cs3, in oneembodiment, are placed in the center section 308 as described above. Inanother embodiment, the capacitors Cs1, Cs2 and Cs3 are placed in ajunction box or other container outside the primary pad 126.

FIG. 7 is a schematic block diagram illustrating a plan view of theembodiment of a low voltage WPT pad 126/127 of FIG. 6. The low voltageWPT pad 126/127 includes a winding 302 divided into four sections withinductances Lp1, Lp2, Lp3 and Lp4 with capacitors Cs1, Cs2 and Cs3connected between the sections. In the embodiment, capacitors Cs1, Cs2and Cs3 are located in the center section 308 and the chimney section306 is modified to allow wiring to pass through to the capacitors Cs1,Cs2 and Cs3. Placing the capacitors Cs1, Cs2 and Cs3 in the centersection 308 is advantageous to provide a more compact WPT pad 126, 128.In other embodiments, the chimney section 306 are modified toaccommodate the conductors connecting the sections of the winding 302 tothe capacitors Cs1, Cs2 and Cs3 by making holes, notches, etc. ratherthan removing a section of the ferrite material of the chimney section306.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A wireless power transfer (“WPT”) pad comprising:a winding comprising a conductor, wherein the conductor is wound in aplanar configuration, the winding comprising a center section aboutwhich the winding is wound; and a ferrite structure comprising: aparallel section located on a side of the winding with at least aportion in parallel with the winding; and a chimney section in magneticcontact with the parallel section and located in the center section ofthe winding, the chimney section extending perpendicular to the parallelsection.
 2. The WPT pad of claim 1, wherein the chimney section extendsin a direction from the parallel section toward the winding and adistance at least a thickness of the winding, the thickness measured ina direction perpendicular to the parallel section of the ferritestructure.
 3. The WPT pad of claim 2, wherein the chimney sectionextends a distance beyond the thickness of the winding.
 4. The WPT padof claim 1, wherein the chimney section is positioned adjacent to thewinding in the center section of the winding.
 5. The WPT pad of claim 1,wherein the ferrite structure further comprises an exterior sectionlocated exterior to an outside edge of the winding, the outside edgedistal to an inside edge adjacent to the center section of the winding,wherein the exterior section is in magnetic contact with the parallelsection and extends perpendicular to the parallel section.
 6. The WPTpad of claim 5, wherein the exterior section extends in a direction fromthe parallel section toward the winding and a distance at least athickness of the winding, the thickness measured in a directionperpendicular to the ferrite structure.
 7. The WPT pad of claim 1,wherein the chimney section comprises a gap, wherein one or morecomponents of the WPT pad are located in the center section of thewinding and one or more conductors from the winding to the one or morecomponents extend through the gap.
 8. The WPT pad of claim 7, whereinthe one or more components comprise one or more capacitors.
 9. The WPTpad of claim 1, wherein an end of the winding is located at an exterioredge of the center section and is wound in a circular pattern thatexpands from a center point within the center section, wherein eachsucceeding lap of the winding is external to a previous lap of thewinding.
 10. The WPT pad of claim 9, wherein each lap of the winding iswithin a same plane, the plane parallel to the parallel section of theferrite structure.
 11. The WPT pad of claim 1, wherein the WPT padcomprises two or more windings, wherein each winding comprises aparallel section of a ferrite structure associated with the winding anda center section, each center section comprising a chimney section ofthe ferrite structure associated with the winding.
 12. The WPT pad ofclaim 11, wherein the ferrite structures of each of the two or morewindings are adjacent to each other and are magnetically coupled. 13.The WPT pad of claim 1, wherein the WPT pad is one of a transmitter padthat transmits power wirelessly to a secondary pad and secondary padthat receives power wirelessly from a transmitter pad.
 14. The WPT padof claim 1, wherein the WPT pad is part of a wireless power transfersystem that transfers power wirelessly to a vehicle.
 15. A wirelesspower transfer (“WPT”) pad comprising: a winding comprising a conductor,wherein the conductor is wound in a planar configuration, the windingcomprising a center section about which the winding is wound; and aferrite structure comprising: a parallel section located on a side ofthe winding with at least a portion in parallel with the winding; achimney section in magnetic contact with the parallel section andlocated in the center section of the winding, the chimney sectionextending perpendicular to the parallel section, wherein the chimneysection is positioned adjacent to the winding in the center section ofthe winding; and an exterior section located exterior to an outside edgeof the winding, the outside edge distal to an inside edge adjacent tothe center section of the winding, wherein the exterior section is inmagnetic contact with the parallel section and extends perpendicular tothe parallel section, wherein the chimney section and the exteriorsection each extend in a direction from the parallel section toward thewinding and a distance at least a thickness of the winding, thethickness measured in a direction perpendicular to the ferritestructure.
 16. The WPT pad of claim 15, wherein the chimney sectioncomprises a gap, wherein one or more components of the WPT pad arelocated in the center section of the winding and one or more conductorsfrom the windings to the one or more components extend through the gap.17. The WPT pad of claim 15, wherein the chimney section and theexterior section each extend a distance beyond the thickness of thewinding.
 18. The WPT pad of claim 15, wherein the WPT pad comprises twoor more windings, wherein each winding comprises a parallel section of aferrite structure associated with the winding and a center section, eachcenter section comprising a chimney section of the ferrite structureassociated with the winding.
 19. The WPT pad of claim 18, wherein theferrite structures of each of the two or more windings are adjacent toeach other and are magnetically coupled.
 20. A wireless power transfer(“WPT”) system comprising: a resonant converter that receives power froma power source; and a WPT pad connected to the resonant converter, theWPT pad receiving power from the resonant converter, the WPT padcomprising: a winding comprising a conductor, wherein the conductor iswound in a planar configuration, the winding comprising a center sectionabout which the winding is wound; and a ferrite structure comprising aparallel section located on a side of the winding with at least aportion in parallel with the winding, and a chimney section in magneticcontact with the parallel section and located in the center section ofthe winding, the chimney section extending perpendicular to the parallelsection.